There are some factors which can mean the actual amount of time waited does not precisely match the amount of time specified:1. Start waiting at the end of the current frame. If you start WaitForSeconds with duration 't' in a long frame (for example, one which has a long operation which blocks the main thread such as some synchronous loading), the coroutine will return 't' seconds after the end of the frame, not 't' seconds after it was called.2. Allow the coroutine to resume on the first frame after 't' seconds has passed, not exactly after 't' seconds has passed.